Infrared radiation (IR) sensors are used in a variety of applications to detect infrared radiation and to provide an electrical output that is a measure of the infrared radiation incident thereon. IR sensors typically use either photonic detectors or thermal detectors for detecting the infrared radiation. Photonic detectors detect incident photons by using the energy of the photons to excite charge carriers in a material. The excitation of the material is then detected electronically. Thermal detectors also detect photons. Thermal detectors, however, use the energy of the photons to increase the temperature of a component. By measuring the change in temperature, the intensity of the photons producing the change in temperature can be determined.
Photonic detectors typically have higher sensitivity and faster response times than thermal detectors. However, photonic detectors must be cryogenically cooled in order to minimize thermal interference, thus increasing the cost, complexity, weight, and power consumption of the device. In contrast, thermal detectors operate at room temperature, thus avoiding the cooling required by photonic detector devices. As a result, thermal detector devices can typically have smaller sizes, lower costs, and lower power consumption than photonic detector devices.
One type of infrared thermal detector is a bolometer device. A bolometer device includes an absorber element for absorbing infrared radiation, a transducer element that has an electrical resistance that varies with temperature, and a substrate. In use, infrared radiation incident upon the bolometer device is absorbed by the absorber element, and the heat generated by the absorbed radiation is transferred to the transducer element. As the transducer element heats in response to the absorbed radiation, the electrical resistance of the transducer element changes in a predetermined manner. By detecting changes in the electrical resistance, a measure of the incident infrared radiation can be obtained.
Bolometer devices must first absorb incident infrared radiation to induce a change in temperature. Typically, however, infrared radiation is dispersed on the absorber as well as portions of the bolometer device that are not configured to absorb infrared radiation, such as the substrate. Accordingly, the efficiency of the bolometer device is less than 100% since the absorber is exposed to only a portion of the incident infrared radiation.
It would be desirable to focus the infrared radiation onto the absorber using a focusing device. Known devices for focusing infrared radiation, however, are very expensive and are typically made using germanium. Furthermore, the cost of known focusing devices for infrared radiation typically exceeds the cost of the bolometer by at least an order of magnitude. Accordingly, while known bolometer devices are effective, there is a constant need to increase the efficiency of bolometer devices, simplify the fabrication, and/or to decrease the production cost of such devices.